Level indicators are commonly used to indicate when the level of fluid has reached a predetermined high level, and usually to also indicate when the level of fluid has reached a predetermined low level. For example, fluid may be pumped or released from a container or no further fluid allowed to enter the container, when the high level is reached. One common use for such level indicators is in underground utility vaults, where a pump is energized to pump water out of the vault when the water level reaches a predetermined height, to prevent immersion of equipment in water. Also, when the water level falls to a low level, the pump is turned off until the water level rises to the high level again.
One type of level indicator includes a fixed housing in the form of a vertical post, with a pair of vertically spaced reed switches that can be activated by a magnet. A float has a hole that receives the post, the float carrying a magnet for activating the switches. When the float rises to a high level, its magnet reaches a position adjacent to the upper switch to activate it, while when the float moves down, its magnet reaches a position adjacent to the lower switch to activate it. The sliding surfaces located at the outside of the post and the inside of the hole that extends through the float, are exposed to the environment. When the float reaches its high level, water covers the lower portion of the post. Chemicals in the water, especially calcium carbonate, can precipitate out of the water, and coat the post and the inside of the float vertical hole. Such coatings can prevent the float from sliding along the post, and result in malfunction with harmful consequences. In the case of underground utility vaults, the water that seeps into the vault, may carry a high percentage of minerals that can precipitate out, due to the water having leached out such chemicals as it migrated through the soil, the concrete walls of the vault, etc. A level indicator of simple construction whose reliability remained high despite the presence of liquid around it which contained chemicals that easily precipitated out of the liquid, would be of value.